The application of metal coatings to substrates is often performed as a batch process operation requiring the submersion of the substrate in a tank of molten metal, sometimes referred to as a "hot dip" coating technique. Such an approach normally does not produce coatings of uniform thickness and can only be used with certain substrates, the sizes of which are small enough to fit into the tanks. Moreover, over extended periods of time, the metal in the tank becomes contaminated and must periodically be discarded and replaced with fresh, clean metal.
Electroplating processes have also been used for such coating purposes. However, while such an electroplating process can produce generally uniform coatings, it is relatively expensive and cannot normally be used to provide relatively thick coatings. Moreover, such process also requires the use of a tank which again limits the size of the substrate being coated.
While spray coating devices have been used to apply coatings, they normally are used for spraying non-metallic paints and often cannot readily achieve a uniform thickness since the spray droplets are generally not uniform in size. Moreover, the apparatus used is often cumbersome and the spray orifices tend to become clogged and must be laboriously cleaned, often in situ, and if the orifices become too clogged, they are usually inconvenient to replace.
It is desirable to develop a coating apparatus which can provide very uniformly sized metal droplets so that, when appropriately applied to a substrate, they produce a coating having uniformly sized droplets and a coating of uniform thickness. Such apparatus should be relatively inexpensive to make and use and be able to coat substrates of various sizes, which substrates may be positioned at various orientations. The apparatus further should permit easy replacement of parts thereof so that maintenance costs can be minimized.